Many electronic and computer-related products such as semiconductors, hard disks and CD-ROMS require highly polished or planarized surfaces in order to achieve optimum performance. In the semiconductor manufacturing industry, for example, silicon workpieces are used in the manufacture of integrated circuit components and the like. The workpieces are known in the industry as "wafers" and typically have a flat, circular disk-like shape. The wafers are initially sliced from a silicon ingot and, thereafter, undergo multiple masking, etching, and dielectric and conductor deposition processes to create microelectronic structures and circuitry on the wafers. The surface of a wafer undergoing these processes typically must be polished or planarized between processing steps to ensure proper flatness, permitting use of photolithographic processes for building additional dielectric and metallization layers on the wafer surface.
Chemical Mechanical Planarization (CMP) machines have been developed to polish or planarize silicon wafer surfaces to the flat condition necessary for manufacture of integrated circuit components and the like. CMP processes and machines are known in the art and are described in several U.S. Patents. Examples include U.S. Pat. No. 4,805,348, issued in February 1989, to Arai, et al.; U.S. Pat. No. 4,811,522, issued in March 1989 to Gill; U.S. Pat. No. 5,099,614, issued in March, 1992 to Arai et al.; U.S. Pat. No. 5,329,732, issued in July, 1994 to Karlsrud et al.; U.S. Pat. No. 5,476,414, issued in December 1995 to Masayoshi et al.; U.S. Pat. Nos. 5,498,196 and 5,498,199, both issued in March, 1996 to Karlsrud et al; and U.S. Pat. No. 5,558,568, issued in September 1996 to Talieh et al.
Known CMP machines and processes typically utilize a wafer carrier or transport apparatus which is positioned above a polishing pad and configured to receive and hold one or more wafers. Typically, the carrier apparatus has multiple heads for holding multiple wafers. In operation, the carrier apparatus is lowered such that the wafers held by the carrier apparatus are pressed against the polishing pad while the polishing pad is rotated about its vertical axis. The wafers may also be rotated about their vertical axes and oscillated radically back and forth over the pad surface to improve polishing effectiveness.
Prior art CMP machines of this sort, while adequate in most respects, do have several drawbacks. The machines are characteristically quite bully and have a sizable "footprint". By this, it is meant that the machines occupy a significant amount of plant floorspace, which is usually limited and expensive. In addition, because the machines have a large footprint, they also are massive and of great weight, increasing the loading on the floor. Another shortcoming of known CMP machines is a difficulty in achieving uniform pressure distribution across the surface of the wafer as it is pressed against the polishing pad. Attaining a uniform pressure distribution is important in that it fosters consistent and uniform polishing across the entire wafer surface. The difficulty in achieving uniform pressure distribution arises from the fact that the entire surface of the wafer is in contact with the polishing pad during polishing operations. Another drawback, arising from the conventional "face down" position that a wafer is held in during polishing, is the difficulty of visually or otherwise monitoring the polishing process for consistency and uniformity.